Pulsed-neutron formation evaluation tools interrogate the formation surrounding the borehole with high energy neutrons produced by a neutron source associated with the tool. Through various types of interactions by the neutrons with elements of the tool, borehole and formation, gamma radiation is created that is incident upon gamma radiation detectors also associated with the tool. Borehole and formation properties can be determined based on the timing of arrival, number of arrivals and/or energy of the gamma radiation.
However, some pulsed-neutron sources are inconsistent in the number neutrons produced from pulse-to-pulse. Thus, a decrease in the amount of gamma radiation sensed by a gamma radiation detector from one interrogation of an earth formation to the next could be caused by a change in a formation property, a change in the number of neutrons produced, or both. Related-art devices attempt to address the neutron source inconsistency by taking ratios of gamma radiation count rates from multiple gamma radiation detectors at multiple axial distances from the neutron source, under the theory the ratios should be less sensitive to neutron source variation. However, while the ratios may be less sensitive, the ratios also dull the sensitivity to formation parameters. Thus, any system or method that helps quantify neutron source inconsistency could improve the sensitivity and accuracy of formation interrogation based on gamma radiation detection.